That headline is from the Sunday Mail - oddly, not on-line but in the print edition. It goes on to mention that it was a Shia mosque and that a 29 year old man (from a gang who "pounced" on the boy) had been arrested and

that police were investigating whether the gang were from a rival Muslim sect.

The police themselves are simply quoted at saying

We are keeping an open mind as to whether it could be racially or religously motivated

The Birmingham attack is mentioned in several other sources listed in a Google News search, but mostly without any mention of the throat slitting (fortunately, the boy wasn't killed) or rival sects. The police's closed open mind is mentioned in all the reports.However, a statement from the mosque with the usual sorrow and regret contains this unusual addition:

You do not represent us.

“You will not divide the unity that we as faith communities enjoy and have worked hard to establish. And you will not stop Islam from being practiced in all its beautiful diversity.”

...that the motive behind the attack was unclear. “Background checks so far have not associated the suspect with any particular mosque or community,” he said. “The board of trustees emphasises that whatever the motive behind this attack, it should not be sensationalised or used as a justification to spread hatred or incite violence. Hussainia mosque will not tolerate the disturbance of the communal harmony between the various communities that share this geography.”

Syed Hassan Abbas was named locally as the victim of the 'ISIS-inspired' stabbing attack outside the Maarif-e-Islam Hussainia Mosque in Herbert Road in Birmingham in the early hours of yesterday.[emphasis in original]